Multiplexer-demultiplexer for microwave antennas

ABSTRACT

The multiplexer-demultiplexer operates in the 3.6 to 4.2, 5.9 to 6.4 and 6.4 to 7.1 kmc frequency bands. For demultiplexing, for example, the system operates as follows: Two serially arranged directional couplers respectively deliver the verticallypolarized signals of the first frequency band and the horizontally-polarized signals of the first frequency band to two outputs of the system, and the remainder of the signals received from the antenna to a polarizer. The latter feeds two waveguides with respective stubs and matching networks, forming the first branches of two Y-junctions; each one of the other branches of these Y-junctions feeds a filter. The four corresponding filters, whose outputs form other outputs of the system, respectively deliver the horizontally-polarized signals in the 6.2 to 6.4 kmc and 6.7 to 7.1 kmc frequency sub-ranges and the verticallypolarized signals in the 5.9 to 6.2 kmc and 6.4 to 6.7 kmc frequency sub-ranges.

United States Patent [191 Hai et al.

[ June 11, 1974 MULTlPLEXER-DEMULTIPLEXER FOR MICROWAVE ANTENNAS Inventors: Nhu Bui l-lai; Alexandre Osias, both of Paris, France Thomas-CSF, Paris, France May 3, 1973 Assignee:

Filed:

.Appl. No.: 356,812

Foreign Application Priority Data May 5. 1972 France 72.!6104 US. Cl. 343/176, 343/756 References Cited UNlTED'STATES PATENTS v 2/l966 Petrilla ct al. 343/175 Primary Examiner-Albert J. Mayer Attorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACT The multiplexer-demultiplexer operates in the 3.6 to 4.2, 5.9 to 6.4 and 6.4 to 7.1 kmc frequency bands. For demultiplexing, for example, the system operates as follows: Two serially arranged directional couplers respectively deliver the vertically-polarized signals of the first frequency band and the horizontally-polarized signals of the first frequency band to two outputs of the system, and the remainder of the signals received from the antenna to a polarizer. The latter feeds two waveguides with respective stubs and matching networks, forming the first branches of two Y-junctions; each one of the other branches of these Y-junctions feeds a filter. The four corresponding filters, whose outputs form other outputs of the system, respectively deliver the horizontally-polarized signals in the 6.2 to 6.4 kmc and 6.7 to 7.1 kmc frequency sub-ranges and the vertically-polarized signals in the 5.9 to 6.2 kmc and 6.4 to 6.7 kmc frequency sub-ranges.

4 Claims, 3 Drawing Figures PATENTEDJUNHIQM 3.816335 sum 1 or 2 Tlg WAVEGUIDE MULTIPLEXER-DEMULTIPLEXER FOR MICROWAVE ANTENNAS The present invention relates to a multiplexerdemultiplexer for a microwave antenna and more especially an antenna intended for the transmission of telephone channels.

The increasing density of radio links is making it necessary, at communication centres, to use progressively larger and larger numbers of antennas. The space available for such antennas on the supporting masts is naturally limited so that the idea of grouping several frequency bands within one and the same antenna, for each of which bands V and H polarizations can be used, has quite naturally arisen.

For short, the frequency bands respectively comprised between 3.6 and 4.2 kmc, 5.9 and 6.4 kmc, 6.4 and 7.1 kmc and 10.7 and 11.7 kmc, will be referred to respectively as the 4 kmc, 6 kmc, 7 kmc and 11 kmc frequency bands.

Various solutions have been proposed. One known multiplexer-demultiplexer makes it possible to carry three frequency bands: 4 kmc, 6 kmc and I1 kmc; the energy in each band is picked off by a directionnal coupler of total coupling type, and the six directional couplers, two for each frequency band, are arranged in series one after the other; this solution cannot be applied where at least two of the frequency bands are close together, the band separation being difficult to achieve at locations where the frequency bands are close together.

Another known multiplexer-demultiplexer makes it possible to handle two frequency bands: 4 kmc and 6 kmc; it employs two directional couplers of total coupling type, associated with the two polarizations of the 4 kmc band, and a polarization duplexer for the 6 kmc;

this solution like the preceding one, does not give good results if the two frequency bands are close together.

Finally, a multiplexer-demultiplexer is known which is designed to handle three frequency bands: 4 kmc, 6 kmc and 7 kmc; and this comprises, in a series arrangement: a port for connection to an antenna, a system of directional couplers, for the 6 kmc and 7 kmc bands, and a polarization duplexer to separate the two 4 kmc band polarizations.

The multiplexer-demultiplexer in accordance with the invention makes it possible to operate in the same frequency bands as the one last-mentioned; it has the advantage of excellent separation or combination between the different bands, on the one hand because the 6 kmc and 7 kmc bands are processed there at locations where the frequencies of the 4 kmc band are not present, and on the other hand because of the structure of the elements designed to separate or diplex the 6 kmc and 7 kmc bands.

In accordance with the invention, there is provided a multiplexer-demultiplexer for a microwave antenna designed to transmit first, second and third frequency bands respectively comprised between 3.6 and 4.2 kmc, 5.9 and 6.4 kmc and 6.4 and 7.1 kmc, said multiplexer-demultiplexer comprising: first coupling means having a first port for coupling to an antenna, and a second port; a first directional coupler having a first port coupled to said second port of said first coupling means, and second and third ports and a second directional coupler having a first port coupled to said third port of said first directional coupler, and second and third ports, one of said directional couplers being designed to transmit to its second port the whole of the vertically-polarized signals in said first frequency band applied to its first port, and the remainder of the signals applied to its first port to its third port, and the other of said directional couplers being designed to transmit to its second port the whole of the horizontallypolarized signals in said first frequency band applied to its first port, and the remainder of the signals applied to its first port to its third port; second coupling means having a first port coupled to said third port of said second directional coupler, and a second port; and a polarizer having first and second polarization ports, and a further port coupled to said second port of said second coupling means; said multiplexer-demultiplexer further comprising: two waveguides each of which is provided with a stub, said two waveguides having respective first ends respectively coupled to said first and second polarization ports of said polarizer and respective second ends; first and second Y-junctions having respective first ports respectively coupled to the second ends of said two waveguides, each of said Y-junctions having two further ports; a first band-pass filter having a first port coupled to one of said further ports of said first Y- junction; and a second band-pass filter having a first port coupled to one of said further ports of said second Y-junction.

The invention will be better understood and other of its features rendered apparent, from a consideration of the ensuing description and the related drawings in which:

FIG. 1 schematically illustrates an antenna compris- I ing a multiplexer-demultiplexer in accordance with the invention;

FIG. 2 illustrates in more detail the multiplexerdemultiplexer of the antenna shown in FIG. 1;

FIG. 3 is the block diagram of one of the elements shown in FIG. 2.

FIG. 1 illustrates in a highly schematic fashion an offset Cassegrain antenna with a multiplexerdemultiplexer in accordance with the invention. A primary source 1, an auxiliary reflector 2 and a main reflector 3, are shown in section and the multiplexerdemultiplexer 5 is shown in side elevation. The multiplexer-demultiplexer comprises a port A coupled to the primary source 1, and six other ports 4 V, 4 H, 6 V, 7 V, 6 H, 7 H, which are defined hereinafter in relation to the other drawings. In FIG. 1, of the transmission and/or reception circuits of the antenna, only the multiplexer-demultiplexer has been shown, the other circuits being conventional in design. By way of indication, the antenna shown in FIG. ll measures 5 m in height and is equivalent, from the performance point of view, to an antenna of the horn-reflector type, 10 rn in height; the multiplexer-demultiplexer 5 measures about 2.5 m. This assembly can be installed at the uper portion of a mast, which portion can also carry all the circuits and devices required for the operation of the antenna, in order to ensure that connections between these various elements do not, by virtue of their length, give rise to parasitic disturbances or any other interference.

FIG. 2 illustrates a more detailed view of the multiplexer-demultiplexer 5 shown in FIG. 1. The multiplexer-demultiplexer taken as an example in this description, is designed to operate simultaneously on the whole frequency plan of the 4 kmc CCIR frequency band for beams of 960 channels per channel group, on half the complete frequency plan of the 6 kmc CCIR frequency band for beams of 1,800 channels per channel group and on half the complete frequency plan of the 7 kmc CCIR frequency band for beams of 2,700 channels per channel group; thus, around 40,000 telephone channels can be passed through this multiplexerdemultiplexer.

The multiplexer-demultiplexer shown in FIG. 2 will be described considering it as a demultiplexer, i.e., from the antenna onwards. It comprises:

the port already defined in connection with FIG. 1;

a circular-to-square transition 10 in which a mode filter is incorporated whose function is to suppress TE and TM modes which are likely to develop at this location; this mode filter is constituted by nickel-chrome coated glass resistors;

a first directional coupler 12 formed by a secondary waveguide, with an output port 4 V, and a main waveguide coupled to the transition 10, and whose main waveguide has a square section and passes all the operating frequencies of the antenna. The magnetic coupling between the main waveguide and the secondary waveguide is effected through holes formed in the common wall of said main and secondary waveguides. The coupler 12 is designed to transmit to the output 4 V of the demultiplexer the whole of the vertically-polarized signals in the 4 kmc frequency band applied to it through the transition 10;

a second coupler 13, identical to the first and whose main waveguide is serially arranged with that of the coupler 12; the main waveguides of the couplers 12 and 13 have a common axis and are turned through 90 in relation to each other about this axis; consequently, the output port, 4 H, of the secondary waveguide of the second coupler is an output for the H polarization of the 4 kmc frequency band;

a square-to-circular transition 14 coupled to the main waveguide of the coupler 13;

a polarizer 15, operating for demultiplexing purposes as a polarization separator, having an input port coupled to the transition 14 and two polarization ports H and V. The polarizer 15 is designed to transmit to its two polarization orts H and V the two linear polarizations H and respectively in the band 5.9-7.l kmc;

a frequency separator 20, coupled to the H port of the polarizer 15, this frequency separator comprising: a waveguide 21 the first end of which is coupled to the H port and which comprises a matching network and a compensating stub 22 adjusted for the 7 kmc band; a Y-junction 23, coupled by the first of its three ports to the second end of the waveguide 24; two filters 24, 25 respectively coupled by their first ports to the second and third ports of Y-junction 23 and provided at their second ports with an insulator designed to improve impedance matching at those of their inputs opposite to the Y-junction. The filters 24 and 25 are respectively adjusted for the 6.7-7.1 kmc frequency subrange, which corresponds to beams carrying 2,700 channels per channel group, and 6.2-6.4 kmc frequency sub-range, which corresponds to beams carrying 1800 channels per channel group; those terminals of the filters 24 and 25 opposite to the Y- junction 23, respectively constitute the output ports 7 H and 6 H of the demultiplexer;

a frequency separator 30 coupled to the V port of the polarizer 15 and formed by elements corresponding to those employed in the frequency separator 20, the reference numbers of these elements being increased by 10 relatively to the corresponding elements of the frequency separator 20, and the output ports 6 H and 7 H being respectively replaced by output ports 6 V and 7 V; the matching network and the stub 32 for the waveguide 31 are adjusted for the 5.9-6.7 kmc frequency band; the filters 34 and 35 are respectively adjusted for the 6.4-6.7 kmc frequency sub-range, corresponding to beams of 2,700 channels per channel group, and the 5.9-6.2 kmc frequency corresponding to beams of 1,800 channels per channel group. The higher frequency sub-ranges of the 6 kmc and 7 kmc bands and the lower frequency sub-ranges of the 6 kmc and 7 kmc bands, which are thus respectively delivered by the frequency separators 20 and 30, contributes, despite the proximity of the 6 kmc and 7 kmc bands, to good quality in the link using this multiplexer-demultiplexer.

FIG. 3 is a schematic illustration of the frequency separator-mixer 20 shown in FIG. 2. The matching network which has been referred to in the context of this frequency separator-mixer during the description of FIG. 2, is marked by the same reference 21 as the waveguide to which it is coupled. Also, shown are the compensating stubs 22, the Y-junction 23, the filters 24 and 25, and the ports 7 H and 6 H plus the port connected, in FIG. 2, to the polarizer and marked here by the letter B.

For claritys sake, the multiplexer-demultiplexer has been described assuming it to be used only for demultiplexing purposes.

As is well known all the elements effecting a separation may be used in the reverse way for multiplexing purposes.

However, in normal operation, corresponding to a good quality link, the antenna is preferably used for a simultaneous multiplexing-demultiplexing, in which one of the frequency separator-mixers 20 and 30 is used as a demultiplexing frequency separator and the other as a multiplexing frequency mixer, whereby each one of the directional couplers, 12 and 13, may be used for transmission or reception, irrespective of how the other coupler is being used, without affecting the quality of the link. The results listed hereinafter correspond to this kind of operation of the multiplexerdemultiplexer.

The frequency separator-mixer 20 covers the frequency subranges of the 6 kmc and 7 kmc bands, with a standing wave ratio of 1.05.

The filters 24, 25 utilized for the higher frequency sub-ranges, are Tschebyscheff cavity filters comprising ten cavities and achieving an attenuation equal to or better than dB for a frequency approximately equidistant from 6.4 and 6.7 kmc, and consequently excellent definition of the filter short-circit planes.

The transmission loss ranges between 0.2 and 0.4 dB and the variation in group delay is less than 0.5 m8.

Similar results are obtained for the lower frequency sub-ranges 5.9-6.2 and 6.4-6.7 kmc, using filters 34, 35 of the Butterworth type.

Self-evidently, the invention isnot limited to the multiplexer-demultiplexer described here, and certain variant embodiments can be employed, as for example the utilization of one of the frequency separator-mixers for transmitting a single frequency band, one of the two filters of this frequency separator-mixer being substituted by a matched load; it is also possible to change over the connection of the frequency separator-mixers 20, 30 to the polarizer 15.

What is claimed is:

1. A multiplexer-demultiplexer for a microwave antenna designed to transmit first, second and third frequency bands respectively comprised between 3.6 and 4.2 kmc, 5.9 and 6.4 kmc and 6.4 and 7.1 kmc, said multiplexer-demultiplexer comprising: first coupling means having a first port for coupling to an antenna, and a second port; a first directional coupler having a first port coupled to said second port of said first coupling means, and second and third ports and a second directional coupler having a first port coupled to said third port of said first directional coupler, and second and third ports, one of said directional couplers being designed to transmit to its second port the whole of the vertically-polarized signals in said first frequency band applied to its first port, and the remainder of the signals applied to its first port to its third port, and the other of said directional couplers being designed to transmit to its second port the whole of the horizontallypolarized signals in said first frequency band applied to its first port, and the remainder of the signals applied to its first port to its third port; second coupling means having a first port coupled to said third port of said second directional coupler, and a second port; and a polarizer having first and second polarization ports, and a further port coupled to said second port of said second coupling means; saidmultiplexer-tiemultiplexer further comprising: two waveguides each of which is provided with a stub, said two waveguides having respective first ends respectively coupled to said first and second polarization ports of said polarizer and respective second ends; first and second Y-junctions having respective first ports respectively coupled to the second ends of said two waveguides, each of said Y-.junctions having two further ports; a first band-pass filter having a first port coupled to one of said further ports of said first Y- junction; and a second band-pass filter having a first port coupled to one of said further ports of said second Y-junction.

2. A multiplexer-demultiplexer as claimed in claim 1, wherein each of said waveguides further comprises a matching network.

3. A multiplexer-demultiplexer as claimed in claim 1, further comprising a third band-pass filter having a first port coupled to the other one of said further ports of said first Y-junction and a fourth band-pass filter having a first port coupled to the other one of said further ports of said second Y-junction, and, wherein said second and third frequency bands being respectively subdivided into a lower sub-range and a higher sub-range, said first, second, third and fourth filters are designed for respectively passing the lower sub-range of said second frequency band, the higher sub-range of said second frequency band, the lower sub-range of said third frequency band and the higher sub-range of said third frequency band.

4. A multiplexer-demultiplexer as claimed in claim 1, wherein said first and second coupling means are respectively circular-to-square and square-to-circular transitions. 

1. A multiplexer-demultiplexer for a microwave antenna designed to transmit first, second and third frequency bands respectively comprised between 3.6 and 4.2 kmc, 5.9 and 6.4 kmc and 6.4 and 7.1 kmc, said multiplexer-demultiplexer comprising: first coupling means having a first port for coupling to an antenna, and a second port; a first directional coupler having a first port coupled to said second port of said first coupling means, and second and third ports and a second directional coupler having a firSt port coupled to said third port of said first directional coupler, and second and third ports, one of said directional couplers being designed to transmit to its second port the whole of the vertically-polarized signals in said first frequency band applied to its first port, and the remainder of the signals applied to its first port to its third port, and the other of said directional couplers being designed to transmit to its second port the whole of the horizontally-polarized signals in said first frequency band applied to its first port, and the remainder of the signals applied to its first port to its third port; second coupling means having a first port coupled to said third port of said second directional coupler, and a second port; and a polarizer having first and second polarization ports, and a further port coupled to said second port of said second coupling means; said multiplexer-demultiplexer further comprising: two waveguides each of which is provided with a stub, said two waveguides having respective first ends respectively coupled to said first and second polarization ports of said polarizer and respective second ends; first and second Y-junctions having respective first ports respectively coupled to the second ends of said two waveguides, each of said Y-junctions having two further ports; a first band-pass filter having a first port coupled to one of said further ports of said first Y-junction; and a second band-pass filter having a first port coupled to one of said further ports of said second Y-junction.
 2. A multiplexer-demultiplexer as claimed in claim 1, wherein each of said waveguides further comprises a matching network.
 3. A multiplexer-demultiplexer as claimed in claim 1, further comprising a third band-pass filter having a first port coupled to the other one of said further ports of said first Y-junction and a fourth band-pass filter having a first port coupled to the other one of said further ports of said second Y-junction, and, wherein said second and third frequency bands being respectively subdivided into a lower sub-range and a higher sub-range, said first, second, third and fourth filters are designed for respectively passing the lower sub-range of said second frequency band, the higher sub-range of said second frequency band, the lower sub-range of said third frequency band and the higher sub-range of said third frequency band.
 4. A multiplexer-demultiplexer as claimed in claim 1, wherein said first and second coupling means are respectively circular-to-square and square-to-circular transitions. 